The increasing demand for energy has lead to renewed interest in non-traditional sources of feedstocks. For instance, coal was used as a source for gaseous fuel ("town gas") during earlier parts of this century. Much work was done at that time to produce higher molecular weight hydrocarbons from the synthesis gas. That work, involving the Fischer-Tropsch reaction based on CO+H.sub.2 chemistry, was revived by Germany during World War II and currently enjoys moderate use at the SASOL plants in South Africa.
Research continues on the CO-H.sub.2 chemistry because of the potential for converting low value feedstocks into higher value products.
Relatively little attention has been paid to the conversion of carbon dioxide into hydrocarbons. Carbon dioxide is the major product of combustion processes and is available at relatively high pressure as a diluent in many gas fields throughout the world.
The catalytic hydrogenation of CO.sub.2 to produce hydrocarbons of various types is known. For instance, in Barrault et al, React. Kinet. Catal. Lett., 17 (3-4) 373 (1981), a process for the production of hydrocarbons using iron-copper supported catalysts. Much of the hydrocarbon made is in the form of methane. Similarly, U.S. Pat. No. 2,692,274 (to Kolbel et al) shows the production of various hydrocarbons from CO.sub.2 and H.sub.2 using an apparently oxidic iron catalyst. Substantial methane appears to be produced.
In Solymosi et al, J. Chem. Soc. Faraday Trans. I, 77, 1003 (1981), the formation of methane from carbon dioxide using ruthenium on alumina is shown.
The disclosure in Pijolat et al, CR. Acad. Sci. Paris, S.II, T295, p. 343 (1982) deals with the hydrogenation of carbon dioxide over iron-on-alumina catalysts. The selectivity of the reaction to methane appears to be greater than 30%. Less than 40% of the C.sub.2 to C.sub.4 fraction is olefinic. See the Table on page 344.
In He et al, ACS Div. Petri. Chem., St. Louis, April 1984, p. 332, a catalyst of ZrO.sub.2 is shown to produce variously methane, methanol, branched alkanes and aromatics when fed CO.sub.2 and/or CO.
A general study of the activities and selectivities of silica-supported Co, Fe and Ru in hydrogenating CO.sub.2 is found in Weatherbee et al, J. Catalysis, 87, 352 (1984). The catalysts produced very high levels of C.sub.1 and low levels of C.sub.2.sup.+ products. The C.sub.2 + olefin production was consequently low, although not specifically discussed.
The use of iron-containing catalysts to produce hydrocarbons from CO and H.sub.2, in the presence of CO.sub.2, has been shown in U.S. Pat. No. 2,486,894 and 2,486,895, both to Watson. There, CO.sub.2 is used to minimize the production of CO.sub.2.
None of the known prior art discloses the production of an iron carbide catalyst via laser pyrolysis for use in the production of hydrocarbons from CO.sub.2 and H.sub.2, much less in the production of olefinic products.
Others have described the use of iron-carbon containing catalysts produced by laser pyrolysis in Fischer-Tropsch reactions. The work of Gupta et al (in U.S. Pat. No. 4,468,474), issued Aug. 28, 1984 and in SPIE 458, Appl. of Lasers to Industrial Chemistry, 131-139 (1984)) shows the production of iron, carbon and silicon-containing catalysts by a laser and the catalysts' subsequent use in the Fischer-Tropsch process. Moderate activity and high C.sub.2 -C.sub.4 olefin selectivity is asserted for the catalysts. Applicants' catalysts contain substantially no silicon.
No known prior art is believed to show the production of olefins from CO.sub.2 and H.sub.2 using the process and the catalyst described below.